Impact of TIM Dielectric Constant on EMI Radiation

Common EMI sources in many systems are integrated circuits (ICs).  ICs are also generators of thermal energy which must be efficiently removed via a heat sink. To enable efficient thermal energy flow a Thermal Interface Material (TIM) is used between the IC and a heat sink. Desirable qualities in a TIM are high thermal conductivity and softness to ensure good physical contact between the IC, heatsink, and TIM. However, it has been found that the electromagnetic properties of the TIM material can increase the EMI radiation leading to failure in regulatory compliance or deterioration in operating efficiency in the device.  This has led many users to demand TIM material with a low dielectric constant (dk). This paper will investigate why the TIM dk could have an impact on EMI radiation.